Big Phil stands between Paul Casey and a shot at The Open

Coasting: Phil Mickelson enjoys the views on day three of the Scottish Open at Castle Stuart yesterday (PA)

Paul Casey's chances of extending his proud run of playing in the last 12 Open Championships will be on a knife edge at Castle Stuart today. Just one 11th-hour ticket to play in the year's third major, which starts at Muirfield on Thursday, is available to the field at this weekend's Scottish Open.

However, to claim it Casey must add the Scottish title to the Irish Open victory he secured at Carton House near Dublin a fortnight ago. And that will be a big ask. A late blip when he ran up a bogey at the par-three 17th green saw Casey sign for a 68 which leaves him five shots off the lead held by Henrik Stenson going into the final round.

And among the players ahead of him is Phil Mickelson, the veteran American left-hander, who sank a 15ft birdie putt on the 18th to complete a six-under 66 that suggests he will head to Murfield in prime form to make amends for his late mistakes at Royal St George's two years ago which handed Darren Clarke the Claret Jug.

But having celebrated his Irish victory, his first in Europe in two years, with a strictly non-golfing trip to Anguilla in the West Indies to attend a friend's wedding, Casey reckons he has the confidence, form and fitness for a Scottish win.

"I am full of energy," said Casey. "I am going to try to push The Open to the back of my mind because the Scottish Open is one of the biggest tournaments of the year on the European Tour.

"But at the same time The Open is the biggest week of the year, and you want to be a part of it. And that win in Ireland has lit a fire in me, I think I can play some great golf for the rest of the year, which is good with Ryder Cup qualifying for next year starting soon."

Mickelson began his third round four shots behind the Scottish overnight leader, Chris Doak, and for the best part of two hours made no progress, much to the disappointment of the huge, sun-soaked crowds following his every pace on the banks of Moray firth.

"I wanted to make a fast start but it didn't happen," said the American later. "In the first eight holes there are two par fives reachable in two and a short driveable par four, but I only played them in level par. But I decided I had to be patient and slow, and then when I finally sank a birdie putt on the eighth green it turned into quite a round."

The wide fairways at Castle Stuart are a far cry from the demands of Muirfield with its carefully placed bunkers at driving distance and knee-high rough, but Mickelson's assessment of his form suggest he is ready to add to his haul of three Masters and one USPGA Championship during his second week in Scotland.

"Off the tee has been my real strength here this week. I know the fairways here are wide but because they are firm you still have to hit them in the right spot. And over the three days I have got the feel of the greens back with my chipping and putting," he said.

Mickelson had barely finished talking when he was joined in the clubhouse lead by Yorkshireman John Parry who like Casey will be chasing an Open ticket but doesn't share the Ryder Cup man's long European pedigree.

Although the 26-year-old won The Vivendi Cup in France in 2010, his rookie year, he later lost his Tour card, which he only got back by winning the Q school qualifier last year. But finishing 28th on his debut last month at the US Open has convinced him he can give Mickelson a run for the money. "I can draw on that win and Q school but the great thing about the US Open was coping in front of huge crowds, and around Castle Stuart anything can happen," he said.

Paul Casey's Open record

2002 Muirfield, missed cut

2003 Royal St George's, missed cut

2004 Royal Troon, 20T

2005 St Andrews, missed cut

2006 Royal Liverpool, 71st

2007 Carnoustie, 27T

2008 Royal Birkdale, 7T

2009 Turnberry, 47T

2010 St Andrews, 3T

2011 Royal St Goerge's, 54T

2012 Royal Lytham, missed cut